RO122093B1 - Method for recovery purification of silver ion from residual solutions - Google Patents

Abstract

The invention relates to a process for recovery purification of silver ion from residual solutions. According to the invention, the process consists in that the silver ion is extracted as anhydrous silver oxalate, in the following optimal reaction conditions: solution pH > 5, 100% oxalic acid in excess and the reaction temperature of 20A C; afterwards the resulting silver oxalate is settled, filtered and dried.

Description

The invention relates to a method of recovering the silver ion from residual solutions, since from the technology of manufacture of passive electronic components, in this case ceramic disk and plate capacitors, a certain percentage of rejected ceramic capacitors having on their surface silver metal coated with a polymerizable resin.

Various methods and processes for extracting silver ion from residual solutions by chemical precipitation, in amorphous forms, with conventional precipitating agents, such as Na ₂ CO ₃ , NaOH and chlorides, with or without chemical coagulation and flocculation, are known. for example with aluminum salts and iron salts.

The disadvantages of the known solutions are related to the amorphous state, the compositional non-uniformity of the extracted forms, the high volume of the precipitate, even at an optimum time of decanting, the low speed of filtration and washing of the precipitate, the chemical instability at atmospheric agents with passage in soluble forms.

The technical problem, which is solved by the invention, relates to the establishment of optimal conditions for the purification of residual solutions with a content of 3 ... 5 g AgNO ₃ / L, resulting from the process of processing with HNO ₃ 35% of the ceramic capacitors.

The method of recovering the silver ion from residual solutions, according to the invention, removes the above disadvantages, in that the residual solution, having a silver nitrate concentration of 3.75 g AgNO ₃ / L, resulted from acid processing 35% of the ceramic capacitors, is treated by mechanical stirring, for 10 minutes, at 20 ° C, with a solution of 0.5 M oxalic acid, in excess of 100% compared to the stoichiometric requirement of the precipitation reaction between the silver cation and the oxalate anion, at a pH of the aqueous silver nitrate solution between 5 and 5.5, obtained after decanting, filtration, washing and drying at room temperature, an anhydrous silver oxalate, at a 97.45% yield.

The method of the invention has the following advantages:

- high decanting, filtration and washing speeds;

- considerably reduced volume of the precipitate;

- high product purity results;

- crystalline form of the final product;

- chemical stability at atmospheric agents (humidity, heat, light, carbon dioxide).

The following are examples of embodiments of the invention, in connection with FIG. 1 and 2, representing:

FIG. 1, dependence of the degree of extraction of the silver of pH;

FIG. 2, dependence of the degree of extraction of silver on the excess of oxalic acid.

For experiments, a solution with a content of 3.75 g AgNO ₃ / dm ³ and a solution of 0.5 M oxalic acid, as a reactant, in a well-defined ratio, at a determined temperature and pH, was used below. stirring.

The silver oxalate precipitate is decanted, filtered and dried.

The silver analysis of the solutions was performed gravimetric and spectrophotometric (with the help of p-dimethyl-aminobenzylidenrodamura).

Thermogravimetric and thermodifferential analysis was performed on a Paulik Paulik Erdely derivatograph.

The experiments aimed to influence the different parameters of the recovery treatment method (pH of the reaction mass, dose of oxalic acid, temperature) on the degree of extraction of silver from the residual solutions.

The experimental data regarding the dependence of the silver extraction degree on the pH of the reaction mass are presented in table 1 and fig. 1.

RO 122093 Β1

Table 1 shows the dependence of the extraction degree on the pH of the reaction mass, at 20 ° C, 10% excess oxalic acid, silver nitrate concentration 3.75 g AgNOj / dm ³ .

Table 1

Nr. crt. pH a,% Nr. crt. pH a,% 1 1 84.93 4 4 91.8 2 2 87.55 5 5 93.36 3 3 89.78 6 5.5 93.36

From FIG. 1 results that the degree of extraction increases with increasing pH, reaching a constant value at pH> 5.

The experimental data regarding the dependence of the degree of extraction of the silver in the form of oxalate are given in table 2 and fig. 2.

Table 2 shows the dependence of the degree of silver extraction on the excess of oxalic acid at 20 ° C, pH = 5, reaction time 10 min and concentration 3.75 g AgNO ₃ / dm ³ .

Table 2

Nr. crt. Excess,% a,% Nr. crt. Excess,% a,% 1 10 84.93 4 80 94.48 2 20 88.51 5 100 97.45 3 30 92.75 6 120 97.45

From FIG. 2 it follows that the optimum extraction degree is achieved at an excess of oxalic acid of more than 100%.

The experimental data regarding the dependence of the temperature extraction of the silver are shown in table 3.

Table 3 shows the dependence of the degree of extraction of the temperature silver, at pH = 5, the concentration of the solution 3.75g AgNO ₃ / dm ³ , reaction time 10 min.

Table 3

Nr. crt. CC a,% 1 20 97.45 2 40 97.67 3 80 98.88

From these data it results that the degree of extraction of silver increases with the increase of temperature, reaching the optimum value at 80 ° C.

The experiments performed on the method of recovery of silver from oxalate residual solutions allowed to determine the optimum conditions for obtaining a maximum degree of separation of silver.

These conditions are: pH> 5, excess of 100% oxalic acid, temperature 20'C.

A well-determined amount of the washed and dried product was dissolved in HNO ₃ concentration 33%. From this solution, silver was determined gravimetrically by precipitation in the form of AgCI. Oxalate was determined permanganometrically.

The data obtained regarding the chemical composition of silver oxalate are given in table 4.

RO 122093 Β1

Table 4

Nr. Ag,% C ₂ O ₄ ² ',% H ₂ O cr,% 1 70.9992 28.9547 .0461 2 70.9950 28.9826 0.0224 3 70.9974 28.9489 .0537 Mediate 70.9972 28.9620 0.0407

From these data it results that the silver oxalate appears in anhydrous form.

Claim

Claims (1)

Method of recovering the silver ion from residual solutions containing silver nitrate, characterized in that the residual solution, having a silver nitrate concentration of 3.75 g AgNO ₃ / L, resulted from processing with 35% nitric acid of the ceramic capacitors, is treated by mechanical stirring, for 10 minutes, at 20 ° C, with a solution of 0.5 M oxalic acid, in excess of 100% compared to the stoichiometric requirement of the precipitation reaction between the silver cation. and the oxalate anion, at a pH of the aqueous silver nitrate solution between 5 and 5.5, obtaining, after decanting, filtration, washing and drying at room temperature, silver oxalate in anhydrous form, at a yield of 97.45%.